The present invention relates to a process for producing a lightweight foamed rubber, which has superior compressive permanent strain, surface appearance and shape retaining property; a process for producing a lightweight foamed rubber; and a sealing material for car use comprising any one of the foamed rubbers obtained according to those processes.
Since an ethylene-xcex1-olefin-non-conjugated diene copolymer rubber has superior properties such as weather resistance, heat resistance and ozone resistance, it has been used as a car part such as a sealing material (for example, a weather strip). The sealing material can be produced from a foamed rubber obtained by foaming and cross-linking a rubber composition containing said copolymer rubber, a foaming agent and a cross-linking agent.
The foamed rubber used for the sealing material is required to have (1) superior compressive permanent strain, because the sealing material has to keep its high sealing property for a long period of time, (2) a high expansion ratio for achieving low cost and lightweight of the sealing material, and (3) superior surface appearance and shape retaining property from a viewpoint of designing property of the sealing material. And recently, these requirements have become greater and greater.
However, foamed rubbers known in the art do not have sufficient processability, foamability with a high expansion ratio, compressive permanent strain, surface appearance and shape retaining property.
An object of the present invention is to provide a process for producing a lightweight foamed rubber, which has superior compressive permanent strain, surface appearance and shape retaining property; and a sealing material for car use comprising the foamed rubber obtained according to said processes.
Another object of the present invention is to provide a process for producing a lightweight foamed rubber; and a sealing material for car use comprising the foamed rubber obtained according to said processes.
The present invention provides a process for producing a foamed rubber having a density of from 0.30 to 0.50 g/cm3, which comprises the step of foaming and cross-linking a rubber composition containing (i) an ethylene-xcex1-olefin-non-conjugated diene copolymer rubber satisfying the following conditions (A) to (D), (ii) a vulcanizing agent and (iii) a foaming agent;
(A) a xylene-insoluble part in the copolymer rubber is from 5 to 20% by weight, or a cyclohexane-insoluble part therein is from 5 to 30% by weight,
(B) a weight ratio of an ethylene polymerization unit/an xcex1-olefin polymerization unit in the copolymer rubber is from 73/27 to 40/60,
(C) a content of a non-conjugated diene polymerization unit in the copolymer rubber is from 18 to 36 in terms of an iodine value, and
(D) Mooney viscosity (ML1+4(121xc2x0 C.)) of the copolymer rubber measured according to JIS-K-6300-Mooney viscosity test is from 50 to 120 (the process being hereinafter referred to as xe2x80x9cProcess 1xe2x80x9d).
The present invention also provides a sealing material for car use, which comprises the foamed rubber obtained according to the above-mentioned Process 1.
Further, the present invention provides a process for producing a foamed rubber having a density of less than 0.50 g/cm3, which comprises the step of foaming and cross-linking a rubber composition containing (i) an ethylene-xcex1-olefin copolymer rubber, (ii) a vulcanizing agent and (iii) a foaming agent having a particle diameter of not more than 10 xcexcm in terms of a median diameter, wherein an amount of the foaming agent exceeds 4.0 parts by weight per 100 parts by weight of the ethylene-xcex1-olefin copolymer rubber(the process being hereinafter referred to as xe2x80x9cProcess 2xe2x80x9d).
Still further, the present invention provides a sealing material for car use, which comprises the foamed rubber obtained according to the above-mentioned Process 2.
According to the above-mentioned Process 1, a lightweight foamed rubber having superior compressive permanent strain, surface appearance and shape retaining property, can be obtained; and according to the above-mentioned Process 2, a lightweight foamed rubber can be obtained. The above-mentioned Processes 1 and 2 are called collectively xe2x80x9cprocess in accordance with the present inventionxe2x80x9d in the present invention.
A xylene-insoluble part contained in the ethylene-xcex1-olefin-non-conjugated diene copolymer rubber used in the Process 1 in accordance with the present invention is from 5 to 20% by weight, and preferably from 6 to 11% by weight; and a cyclohexane-insoluble part therein is from 5 to 30% by weight, and preferably from 5 to 15% by weight. When respective insoluble parts are less than 5% by weight, an expansion ratio is so low that any lightweight foamed rubber cannot be obtained, and the obtained foamed rubber does not have superior shape retaining property. When the insoluble parts exceed 20% by weight or 30% by weight, respectively, the rubber composition used in the present invention does not have such a good kneading processability that the obtained foamed rubber does not have superior surface appearance.
A weight ratio of an ethylene polymerization unit/an xcex1-olefin polymerization unit in the ethylene-xcex1-olefin-non-conjugated diene copolymer rubber used in the present invention is from 73/27 to 40/60, and preferably from 67/33 to 45/55. In the present invention, xe2x80x9cmonomer polymerization unitxe2x80x9d such as xe2x80x9cethylene polymerization unitxe2x80x9d is referred hereinafter to xe2x80x9cmonomer unitxe2x80x9d. When the weight ratio of the ethylene unit exceeds 73, the obtained foamed rubber does not have superior compressive permanent strain at a low temperature, or does not have superior recovery property. When the weight ratio of the ethylene unit is lower than 27, dispersion of a reinforcing agent such as carbon black and an inorganic filler in the rubber composition used in the present invention is so insufficient that the obtained foamed rubber does not have superior surface appearance.
A content of the non-conjugated diene unit contained in the ethylene-xcex1-olefin-non-conjugated diene copolymer rubber used in the Process 1 is from 18 to 36, and preferably from 20 to 29, in terms of an iodine value. When the iodine value is less than 18, a cross-linking density of the obtained foamed rubber is so low that the obtained foamed rubber does not have superior compressive permanent strain. Even if the iodine value exceeds 36, the obtained foamed rubber does not have any further improved compressive permanent strain.
Mooney viscosity of the ethylene-xcex1-olefin-non-conjugated diene copolymer rubber used in the Process 1 is from 50 to 120, and preferably from 75 to 95. When the Mooney viscosity is less than 50, a gas generated by decomposition of a foaming agent used for foaming the rubber composition is hardly retained in the composition, so that any lightweight foamed rubber cannot be obtained. When the Mooney viscosity exceeds 120, the rubber composition used in the present invention does not have good kneading processability and extrusion processability.
In the present invention, the xylene-insoluble part and the cyclohexane-insoluble part are measured according to a method comprising the steps of:
(1) cutting the ethylene-xcex1-olefin-non-conjugated diene copolymer rubber to obtain pieces, each of which has a size of nearly 1 mm square,
(2) weighing about 0.5 g of the pieces with a precision of 0.1 mg, and assigning the weight to be xe2x80x9cAxe2x80x9d g,
(3) putting the weighed pieces and 150 ml of xylene (250 ml of cyclohexane when the cyclohexane-insoluble part is measured) containing 0.1% by weight of 2,6-di-tert-buty-4-methyl phenol (antioxidant) in a 300 ml Erlenmeyer flask equipped with a ground stopper (500 ml Erlenmeyer flask equipped with a ground stopper when the cyclohexane-insoluble part is measured),
(4) equipping said Erlenmeyer flask with a reflux condenser, and dipping it in a water bath at 100xc2x0 C. for 6 hours to reflux (this step is not necessary when the cyclohexane-insoluble part is measured),
(5) taking the Erlenmeyer flask equipped with a reflux condenser out of the water bath, and leaving it at ambient temperature for 30 minutes (when the cyclohexane-insoluble part is measured, leaving the Erlenmeyer flask of the step 3 at 25xc2x0 C. for 24 hours),
(6) shaking the Erlenmeyer flask for 1 hour with a shaker at a rotating speed of 120 rpm,
(7) on the other hand, weighing a 120 mesh wire net with a precision of 0.1 mg, and assigning the weight to be xe2x80x9cBxe2x80x9d g,
(8) filtering the liquid in the Erlenmeyer flask of the step 6 using said wire net,
(9) adding about 20 ml of xylene (about 40 ml of cyclohexane when the cyclohexane-insoluble part is measured) to the Erlenmeyer flask, in which a trace amount of a solid remains, and further filtering the remaining solid to collect on the wire net,
(10) drying the solid-holding wire net at 60 to 90xc2x0 C. for 3 hours,
(11) leaving the dried solid-holding wire net in a desiccator at ambient temperature for about 30 minutes,
(12) weighing the solid-holding wire net with a precision of 0.1 mg, and assigning the weight to be xe2x80x9cCxe2x80x9d g, and
(13) calculating the xylene-insoluble part or the cyclohexane-insoluble part according to the following equation:
xe2x80x83Insoluble part (%)=100(Cxe2x88x92B)/A. 
The ethylene-xcex1-olefin copolymer rubber used in the Process 2 in accordance with the present invention means an ethylene-xcex1-olefin copolymer rubber or the above-mentioned ethylene-xcex1-olefin-non-conjugated diene copolymer rubber.
Examples of the xcex1-olefin of the ethylene-xcex1-olefin copolymer rubber and the ethylene-xcex1-olefin-non-conjugated diene copolymer rubber are propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene and 1-decene, and a combination of two or more thereof. Of these, propylene and 1-butene are preferable.
In the present invention, the xe2x80x9cnon-conjugated dienexe2x80x9d of said copolymer rubber means not only a non-conjugated diene but also a non-conjugated polyene such as a non-conjugated triene. Examples of such compounds are linear non-conjugated dienes such as 1,4-hexadiene, 1,6-octadiene, 2-methyl-1,5-hexadiene, 6-methyl-1,5-heptadiene and 7-methyl-1,6-octadiene; cyclic non-conjugated dienes such as cyclohexadiene, dicyclopentadiene, methyltetraindene, 5-vinylnorbornene, 5-ethylidene-2-norbornene and 6-chloromethyl-5-isopropenyl-2-norbornene; trienes such as 2,3-diisopropylidene-5-norbornene, 2-ethylidene-3-isopropylidene-5-norbornene, 2-propenyl-2,2-norbornadiene, 1,3,7-octatriene and 1,4,9-decatriene; 5-vinyl-2-norbornene; 5-(2-propenyl)-2-norbornene; 5-(3-butenyl)-2-norbornene; 5-(4-pentenyl)-2-norbornene; 5-(5-hexenyl)-2-norbornene; 5-(5-heptenyl)-2-norbornene; 5-(7-octenyl)-2-norbornene; 5-methylene-2-norbornene; 6,10-dimethyl-1,5,9-undecatriene; 5,9-dimethyl-1,4,8-decatriene; 4-ethylidene-8-methyl-1,7-nonadiene; 13-ethyl-9-methyl-1,9,12-pentadecatriene; 5,9,13-trimethyl-1,4,8,12-tetradecadiene; 8,14,16-trimethyl-1,7,14-hexadecatriene; and 4-ethylidene-12-methyl-1,11-pentadecadiene; and a combination of two or more thereof. A preferable compound is 5-ethylidene-2-norbornene or dicyclopentadiene or a combination of both.
A process for producing the ethylene-xcex1-olefin copolymer rubber or the ethylene-xcex1-olefin-non-conjugated diene copolymer rubber is not particularly limited. Said copolymer rubbers can be produced by a conventional process using a conventional catalyst such as a titanium catalyst, a vanadium catalyst and a metallocene catalyst.
When the ethylene-xcex1-olefin copolymer rubber is used in the Process 2, a molar ratio of an ethylene unit/an xcex1-olefin unit therein is usually 1/(0.1 to 1); and when the ethylene-xcex1-olefin-non-conjugated diene copolymer rubber is used in the Process 2, a molar ratio of an ethylene unit/a non-conjugated diene unit therein is usually 1/(0.005 to 0.2).
Mooney viscosity at 121xc2x0 C. of said copolymer rubber is usually from 5 to 200, and preferably from 20 to 180. When the viscosity is less than 5, it is difficult to make a ribbon used for continuously ribbon-feeding of the rubber composition to a cold flow or a molding machine, or an extrudate of the rubber composition is deformed. When the viscosity exceeds 200, productivity of the foamed rubber may decrease.
In a process in accordance with the present invention, the ethylene-xcex1-olefin-non-conjugated diene copolymer rubber or the ethylene-xcex1-olefin copolymer is used in combination with a foaming agent and a vulcanizing agent (a cross-linking agent) to make a rubber composition. The ethylene-xcex1-olefin-non-conjugated diene copolymer rubber or the ethylene-xcex1-olefin copolymer can be used in combination with an appropriate compounding agent known in the production of a foamed rubber such as foaming coagents, plasticizers, vulcanization accelerators (cross-linking accelerators), vulcanization coagents (cross-linking auxiliaries), fillers, flame retarders, antioxidants, tackiness substances (for example, polybutene and rosin), rubber surface lubricants (for example, stearic acid), cross-linking activators (for example, polyethylene glycol), water absorbents (for example, calcium oxide) and resins (for example, polyethylene and polypropylene).
Examples of the foaming agent are sodium hydrogen carbonate, sodium carbonate, ammonium hydrogen carbonate, ammonium carbonate, ammonium nitrite, N,Nxe2x80x2-dimethyl-N,Nxe2x80x2-dinitroso-telephthalamide, N,Nxe2x80x2-dinitroso-pentamethylene-tetramine, azodicarbonamide, azobisisobutyronitrile, azocyclohexylnitrile, azodiaminobenzene, barium azodicarboxylate, benzenesulfonyl hydrazide, toluenesulfonyl hydrazide, toluenesulfonyl hydrazide derivatives, p-toluenesulfonyl semicarbazide, 4,4xe2x80x2-oxybis(benzenesulfonyl hydrazide), diphenylsulfone-3,3xe2x80x2-disulfonyl hydrazide, calcium azide, 4,4xe2x80x2-diphenyl-disulfonyl azide, p-toluenesulfonyl azide, p-toluenesulfonyl acetonehydrazone and hydrazodicarbonamide, and a combination of two or more thereof. Of these, a foaming agent having a particle diameter of not more than 10 xcexcm, preferably not more than 5 xcexcm in terms of a median diameter is preferable from a viewpoint of increasing an expansion ratio.
A preferable amount of the foaming agent used in the Process 1 is from 0.5 to 20 parts by weight per 100 parts by weight of the ethylene-xcex1-olefin-non-conjugated diene copolymer rubber. When the amount is less than 0.5 part by weight, an expansion ratio of the obtained foamed rubber may be lowered. When the amount exceeds 20 parts by weight, the obtained foamed rubber may not have superior surface appearance.
An amount of the foaming agent used in the Process 2 exceeds 4.0 parts by weight per 100 parts by weight of the ethylene-xcex1-olefin copolymer, and preferably not less than 5 parts by weight from a viewpoint of obtaining a high expansion ratio. It is recommendable to use 4,4xe2x80x2-oxybis(benzenesulfonyl hydrazide) as the foaming agent.
The foaming agent may be used in combination with foaming coagents. Examples of the foaming coagents are urea compounds; zinc oxide; inorganic salts such as tribasic lead sulfate; metal soap such as zinc stearate and lead stearate; and salicylic acid.
Examples of the plasticizers are process oil, lubricating oil, paraffin, fluidized paraffin, petroleum asphalt, vaseline, coal tar pitch, castor oil, linseed oil, factice, beeswax, ricinolicacid, palmitic acid, barium stearate, calcium stearate, zinc laurate, atactic polypropylene and cumaron indene resins. Of these, process oil is particularly preferable. An amount of the plasticizers used is usually from 10 to 150 parts by weight, preferably from 30 to 150 parts by weight, and more preferably from 50 to 150 parts by weight, per 100 parts by weight of the ethylene-xcex1-olefin-non-conjugated diene copolymer rubber or the ethylene-xcex1-olefin copolymer rubber.
Preferable examples of the vulcanizing agent are sulfur; sulfur chloride; sulfur dichloride; 4,4xe2x80x2-dithiodimorpholine; morpholine disulfide; alkylphenol disulfide; tetramethylthiuram disulfide; selenium dimethyldithiocarbamate; and organic peroxides such as dicumyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, 2,5-dimethyl-2,5-(t-butylperoxy)hexyne-3, di-t-butylperoxide, di-t-butylperoxide-3,3,5-trimethylcyclohexane and t-butylhydroperoxide. Of these, preferred are sulfur, dicumyl peroxide, di-t-butylperoxide and t-butylperoxide-3,3,5-trimethylcyclohexane.
Sulfur is used in an amount of usually from 0.1 to 10 parts by weight, and preferably from 0.5 to 5 parts by weight, per 100 parts by weight of the ethylene-xcex1-olefin-non-conjugated diene copolymer rubber or the ethylene-xcex1-olefin copolymer rubber. The organic peroxide is used in an amount of usually from 0.1 to 15 parts by weight, and preferably from 0.5 to 8 parts by weight, per 100 parts by weight of said copolymer rubber.
The above-mentioned sulfur or sulfur-containing compound may be used in combination with a vulcanization accelerator or a vulcanization coagent. Examples of the vulcanization accelerator are N-cyclohexyl-2-benzothiazole-sufenamide, N-oxydiethylene-2-benzothiazole-sulfenamide, N,N-diisopropyl-2-benzothiazole-sulfenamide, 2-mercaptobenzothiazole, 2-(2,4-dinitrophenyl)mercaptobenzothiazole, 2-(2,6-diethyl-4-morpholinothio)benzothiazole, dibenzothiazyl-disulfide, diphenylguanidine, triphenylguanidine, di-o-tolylguanidine, o-tolyl-bi-guanide, diphenylguanidine-phthalate, an acetaldehyde-aniline reaction product, a butylaldehyde-aniline condensate, hexamethylenetetramine, acetaldehyde ammonia, 2-mercaptoimidazoline, thiocarbaniride, diethylthiourea, dibutylthiourea, trimethylthiourea, di-o-tolylthiourea, tetramethylthiuram monosulfide, teramethylthiuram disulfide, teraethylthiuram disulfide, terabutylthiuram disulfide, dipentamethylenethiuram tetrasulfide, zinc dimethyldithiocarbamate, zinc diethylthiocarbamate, zinc di-n-butylthiocarbamate, zinc ethylphenyldithiocarbamate, zinc butylphenyldithiocarbamate, sodium dimethyldithiocarbamate, selenium dimethyldithiocarbamate, tellurium diethyldithiocarbamate, zinc dibutylxanthate and ethylenethiourea. The vulcanization accelerator is used in an amount of from 0.1 to 20 parts by weight, and preferably from 0.2 to 10 parts by weight, per 100 parts by weight of the ethylene-xcex1-olefin-non-conjugated diene copolymer rubber or the ethylene-xcex1-olefin copolymer rubber.
Examples of the vulcanization coagent are metal oxides such as magnesium oxide and zinc oxide. Of these, preferred is zinc oxide. The vulcanization coagent is used usually in an amount of from 3 to 20 parts by weight per 100 parts by weight of the ethylene-xcex1-olefin-non-conjugated diene copolymer rubber or the ethylene-xcex1-olefin copolymer rubber.
The peroxide may be used in combination with cross-linking coagents such as sulfur, quinonedioxime compounds (for example, p-quinonedioxime), polyethylene glycol dimethacrylate, diallyl phthalate, triallyl cyanurate and divinylbenzene.
Preferable examples of the fillers are carbon black usually used in the field of rubber such as SRF (N770), GPF (N660), FEF (N550), HAF (N330), ISAF (N220), SAF (N110), ET (N880) and MT (N990); and inorganic fillers such as fine grain silicic acid, calcium carbonate, talc and clay. An amount of the fillers used is preferably from 30 to 300 parts by weight, and more preferably from 70 to 200 parts by weight, per 100 parts by weight of the ethylene-xcex1-olefin-non-conjugated diene copolymer rubber or the ethylene-xcex1-olefin copolymer rubber.
A density of the foamed rubber obtained according to the Process 1 is from 0.30 to 0.50 g/cm3, and preferably from 0.34 to 0.42 g/cm3. When the density is less than 0.30 g/cm3, any foamed rubber having good compressive permanent strain cannot be obtained. When the density exceeds 0.50 g/cm3, a lightweight foamed rubber cannot be obtained.
A density of the foamed rubber obtained according to the Process 2 is less than 0.50 g/cm3. When the density is not less than 0.50 g/cm3, any foamed rubber having a high expansion ratio (in other words, any lightweight foamed rubber) cannot be obtained.
The rubber composition used in the present invention can be obtained by kneading respective components to make the same using both Banbury mixer and a roll, or using both a kneader and a roll. Said rubber composition has superior processability.
It is possible to produce a lightweight foamed rubber, which has superior compressive permanent strain, surface appearance and shape retaining property, by foaming and cross-linking said rubber composition using an apparatus such as an oven, a continuous hot air cross-linking apparatus, a microwave heating apparatus, a glass beads fluidized bed, a molten salt vessel and a hot mold. The obtained foamed rubber is most suitable as a sealing material for car use.